Air-Fuel Ratio (AFR) Calculator

Calculate air-fuel ratio, lambda, and stoichiometric values for different fuels.

Enter air and fuel amounts, select fuel type, and get instant AFR, lambda, and mixture analysis.

Examples

See how to use the AFR Calculator for different fuels and scenarios.

Gasoline - Ideal Combustion

Gasoline

Calculate the AFR for 14.7g air and 1g gasoline (stoichiometric).

Fuel Type: Gasoline

Air Amount: 14.7 g

Fuel Amount: 1 g

Diesel - Lean Mixture

Diesel

Calculate the AFR for 20g air and 1g diesel.

Fuel Type: Diesel

Air Amount: 20 g

Fuel Amount: 1 g

LPG - Rich Mixture

LPG

Calculate the AFR for 12g air and 1g LPG.

Fuel Type: LPG

Air Amount: 12 g

Fuel Amount: 1 g

Hydrogen - Stoichiometric

Hydrogen

Calculate the AFR for 34.3g air and 2g hydrogen.

Fuel Type: Hydrogen

Air Amount: 34.3 g

Fuel Amount: 2 g

Other Titles
Understanding Air-Fuel Ratio (AFR): A Comprehensive Guide
Master the science of combustion, lambda, and mixture optimization.

What is Air-Fuel Ratio (AFR)?

  • Definition and Importance
  • Stoichiometric Ratio
  • Rich and Lean Mixtures
The air-fuel ratio (AFR) is the mass ratio of air to fuel present in a combustion process. It is a critical parameter in engines, burners, and chemical reactions involving fuels.
Stoichiometric AFR
The stoichiometric AFR is the ideal ratio where all fuel is burned using all available oxygen, leaving no excess air or fuel. For gasoline, this is typically 14.7:1.
Rich and Lean Mixtures
A mixture is 'rich' if there is excess fuel (AFR < stoichiometric), and 'lean' if there is excess air (AFR > stoichiometric).

Common Stoichiometric AFR Values

  • Gasoline stoichiometric AFR is 14.7:1.
  • Diesel stoichiometric AFR is 14.5:1.

Step-by-Step Guide to Using the AFR Calculator

  • Input Selection
  • Calculation Process
  • Result Interpretation
Input Selection
Select the fuel type, enter the air and fuel amounts, and choose the appropriate units for each.
Calculation Process
The calculator computes the AFR by dividing the air amount by the fuel amount, then compares it to the stoichiometric value for the selected fuel.
Result Interpretation
Results include the calculated AFR, stoichiometric AFR, lambda, mixture type, and deviation from ideal.

Sample Calculations

  • Input: 14.7g air, 1g gasoline → AFR = 14.7 (stoichiometric)
  • Input: 20g air, 1g diesel → AFR = 20 (lean)

Real-World Applications of AFR

  • Engine Tuning
  • Emissions Control
  • Laboratory Analysis
Engine Tuning
AFR is crucial for optimizing engine performance, fuel economy, and emissions in automotive and industrial engines.
Emissions Control
Proper AFR ensures complete combustion, reducing harmful emissions such as CO, NOx, and unburned hydrocarbons.
Laboratory Analysis
Chemists use AFR calculations to design and analyze combustion experiments and fuel efficiency tests.

Practical Uses

  • Tuning a gasoline engine for optimal AFR.
  • Measuring emissions in a diesel generator.

Common Misconceptions and Correct Methods

  • AFR vs. Lambda
  • Unit Consistency
  • Mixture Interpretation
AFR vs. Lambda
AFR is fuel-specific, while lambda is a universal indicator of mixture richness or leanness. Lambda = 1 means stoichiometric.
Unit Consistency
Always use consistent units for air and fuel amounts to avoid calculation errors.
Mixture Interpretation
A rich mixture is not always better for power; it can increase emissions and reduce efficiency.

Misconceptions

  • Using kg for air and g for fuel gives incorrect AFR.
  • Lambda = 0.9 means rich; lambda = 1.1 means lean.

Mathematical Derivation and Examples

  • AFR Formula
  • Lambda Calculation
  • Deviation Analysis
AFR Formula
AFR = Air Amount / Fuel Amount. Both must be in the same unit (g, kg, or lb).
Lambda Calculation
Lambda = AFR / Stoichiometric AFR. Lambda = 1 is ideal; <1 is rich, >1 is lean.
Deviation Analysis
Deviation (%) = 100 × (AFR - Stoichiometric AFR) / Stoichiometric AFR.

Mathematical Examples

  • AFR = 14.7 / 1 = 14.7 (stoichiometric for gasoline)
  • Lambda = 13 / 14.7 ≈ 0.88 (rich)